1. Field of the Invention
The present invention is related to a fixing device and an image forming apparatus, and in particular to, the fixing device which fixes an unfixed image onto a recording medium, and the image forming apparatus such as a copier, a facsimile, a printer, a printing machine, and the like including the fixing device.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as a copier, a facsimile, a printer, and a printing machine, or the like, a copied material or a printed material is generated by heating and fixing an unfixed image which is transferred and is supported on a recording medium.
In a heating and fixing process, by a fixing roller and a fixing nip part formed by a pressure roller pressing and contacting the fixing roller, the recording medium supporting the unfixed image is clamped and heated. By this process, a developer for forming the unfixed image such as a toner is melted and softened. When the developer is infiltrated into the recording medium, the unfixed image is fixed on the recording medium.
In the fixing device, as the recording medium on which an image is fixed, various recording media such as a thin paper, a regular paper, a thick paper, and the like are used. If a constant pressure and heat are applied at the fixing nip part, a fixing performance is not sufficiently stabilized. Japanese Laid-open Patent Application No. 2009-14829 discloses a fixing apparatus in that a position of a pressing member is changed with respect to the a fixing member for pressing and heating.
The fixing apparatus disclosed in Japanese Laid-open Patent Application No. 2009-14829 sets a preferred pressure at the fixing nip part depending on a type of a recording medium being conveyed. As a result, it is possible to prevent an occurrence of a wrinkle to the recording medium and from an insufficient fixing or an excess fixing of toner transferred on the recording medium. Thus, the fixing performance of the toner transferred on the recording medium is improved at the fixing nip part of the fixing device.
In the image forming apparatus including the fixing roller, in order to improve a separation between the recording medium and the fixing roller when the recording medium is passing through the fixing nip part, a curvature of the fixing nip part is set to be a large value. However, there is a problem in that the recording medium passing through the fixing nip part is ejected in a curled state.
In order to solve this problem, Japanese Laid-open Patent Application No. 2006-23427 discloses an image forming apparatus including a correction nip part formed by a pair of decurl rollers having a curvature in an opposite direction to the fixing nip part.
The image forming apparatus disclosed in Japanese Laid-open Patent Application No. 2006-23427 includes a fixing nip part which heats and fixes the unfixed image onto the recording medium, and a decurl mechanism which is formed by a correction nip part for correcting a curl of the recording medium formed when the recording medium passes through the fixing nip part and a guide which is arranged at a downward side of conveying the recording medium at the correction nip part and adjusts a conveying direction of the recording medium passing through the correction nip part. Accordingly, the conveying direction of the recording medium is changed by the guide while passing through the correction nip part, and the curl of the recording medium is corrected.
Moreover, in general, a convey path of the recording medium rises perpendicularly at the fixing nip part from a bottom part of the image forming apparatus, and goes toward one of paper ejecting ports. Thus, if it is attempted to correct all curls of the recording medium, the decurl mechanism is required to be arranged immediately after the fixing nip part or to be arranged at each of the paper ejecting ports.
However, if the decurl mechanism is arranged immediately after the fixing nip part, a space is required in a longitudinal direction. As a result, a main body of the image forming apparatus becomes a larger size. Instead, if the decurl mechanism is arranged at each of the paper ejecting ports, the image forming apparatus becomes the larger size as a whole and expense is increased. Thus, the decurl mechanism is arranged at a regular paper ejecting port alone which is frequently used. In a case of ejecting a paper sheet from any one of paper ejecting ports other than the regular paper ejecting port, the recording medium is curled and a jam may be caused.